Re: abysmal performance

[Bernhard Schmidt <berni@birkenwald.de>]

Am 03.05.2011 13:08, schrieb Chris Mason:

>> defragging btrfs does not seem to work for me. I have run the filefrag
>> command over the whole fs and (manually) tried to defrag a few heavily
>> fragmented files, but I don't get it to work (it still has the same
>> number of extends and they are horrently uncorrelated)
>>
>> root@schleppi:~# filefrag
>> /usr/lib/x86_64-linux-gnu/gcc/x86_64-linux-gnu/4.4/cc1
>> /usr/lib/x86_64-linux-gnu/gcc/x86_64-linux-gnu/4.4/cc1: 72 extents found
>> root@schleppi:~# btrfs filesystem defrag
>> /usr/lib/x86_64-linux-gnu/gcc/x86_64-linux-gnu/4.4/cc1
>> root@schleppi:~# filefrag
>> /usr/lib/x86_64-linux-gnu/gcc/x86_64-linux-gnu/4.4/cc1
>> /usr/lib/x86_64-linux-gnu/gcc/x86_64-linux-gnu/4.4/cc1: 72 extents found
>>
>> I'm using Ubuntu Natty (2.6.38.4) and tried both btrfs-tools from Natty
>> (201006xx) and from Debian experimental (git from 20101101). Both show
>> the same symptoms. I don't think fragmentation is bad on this box (due
>> to having an SSD), but my system at home is getting dog slow and I'd
>> like to try that when I come home end of the week.
> 
> Do you have compression on?

Yes. lzo to be exact.

> The file the defrag ioctl works is that it schedules things for defrag
> but doesn't force out the IO immediately unless you use -f.
> 
> So, to test the result of the defrag, you need to either wait a bit or
> run sync.

Did so, no change. See my reply to cwillu for the data.

I usually mount my / without any compression option and did "mount -o
remount,compress=lzo /" before. I cannot reboot at the moment and I did
not find any option to disable compression again. There does not seem to
be a "nocompress" or "compress=[none|off]" option. Is this correct?

Bernhard